This invention concerns machines for the manufacture of thermoformed plastic containers, such as cups, and more particularly machines for forming a bead on the lip of the molded cup, generally referred to as lip curling or rolling machines. Such apparatus has been known for many years in the industry, and is described in U.S. Pat. No. 3,337,919 issued on Aug. 29, 1967 for a "Container Rim Beading Apparatus". This type of machine includes a set of feed rollers receiving a continuous train of nested cups extending horizontally, which are advanced at a carefully set rate through a heating oven to soften the cup rims and thence into a lip curling screw mechanism which forms the heated rims into a smooth lip. The feed rollers also rotate the cup stack at a rate matched to the rotation of the curling screws for proper feed into the curling screws.
This arrangement has performed well over the years and has been widely used in the industry.
Many of these machines are designed to be adjustable for different container configurations. The adjustable size require significant maintenance support, particularly in being initially set up for a run of each size and type of container. The feed rollers, typically three in number, are each mounted for an individual pivotal adjustment about an axis extending normally to the center axis of a circle about which the feed rollers are arranged. The degree of tilt of the rollers with respect to the path of the nested cups controls the rate of feed. It is critical that the feed rate be set in close correspondence to the rate of advance through the curling screws in order that the cups stay fully nested while in the oven for proper heating of the rim only. That is, if the feed rate is too slow, the cups become separated and the cup bodies become exposed to be heated and softened. The feed of the cups also must not be too high as this will unduly compress the stack and cause twisting and snaking of the stack in the oven. The proper feed rate is mostly a function of the stack height of a given cup configuration, as the rate of feed of the stack of cups into the curling screws necessarily varies with the number of cups per unit length in the stack.
A slow, painstaking adjustment of each individual feed roller has in the past been necessary, carried out while the machine is shut down, adversely affecting productivity. This process would typically take several hours for an initial set up.
It is also difficult to repeat a given set up such that to some degree a trial and error process is involved.
It is desirable that different sizes of cups will be run on the same machine, such that the radial spacing of the feed rollers, must also be set individually with the machine shuts down, making it impossible for the center axis around which the feed rollers are arranged to be located exactly on the center axis of the guide bars extending through the oven. This discrepancy substantially limits the production rate of the machine, particularly when other inaccuracies are present.
Adjustments in the feed diameter also affects the feed rate, requiring both to be painstakingly adjusted alternately.
Previous attempts to provide an improved method adjustment of the feed rollers have not been successful.
Accordingly, it is the object of the present invention to provide mechanisms for simultaneously adjusting each of the feed roller angle and the feed roller diameter in a lip forming machine of the type described, which allows for much quicker adjustments and that both said adjustments can be made while the machine is in operation.
Another object is to provide an adjustable feed roller mechanism which maintains an accurate alignment of the center axis of the rollers with the other components of the machine to allow high production rates.
It is a further object to provide such mechanisms which allow a given set up to be reliably and quickly reset at a later time to minimize changeover to different container types and/or sizes.